Asset management & maintenance
MTBF and MTTR: measuring equipment reliability and repair speed
How to calculate MTBF, MTTR and availability, with worked examples, what the numbers tell you, data you need and how to improve each one.
MTBF (mean time between failures) measures how long equipment runs, on average, before it breaks down. MTTR (mean time to repair) measures how long, on average, it takes to get it running again. Together they describe reliability and maintainability, and they explain most of a machine's availability. They are standard maintenance KPIs for plants, fleets, facilities and any operation that depends on equipment.
The formulas
| Metric | Formula | Higher or lower is better |
|---|---|---|
| MTBF | Total operating time ÷ number of failures | Higher |
| MTTR | Total repair time ÷ number of repairs | Lower |
| Availability | MTBF ÷ (MTBF + MTTR) | Higher |
MTTF (mean time to failure) is used for non-repairable items, such as bulbs or some sensors, which are replaced rather than repaired.
Worked example
A packaging machine is scheduled to run 720 hours in a month. It failed 4 times, with a total of 20 hours of repair downtime.
- Operating time = 720 − 20 = 700 hours
- MTBF = 700 ÷ 4 = 175 hours
- MTTR = 20 ÷ 4 = 5 hours
- Availability = 175 ÷ (175 + 5) = 97.2%
If preventive maintenance cuts failures to 2 per month with the same 5 hours per repair, operating time becomes 710 hours, MTBF rises to 355 hours and availability to about 98.6%.
What the numbers tell you
| Situation | Likely issue | Where to look |
|---|---|---|
| Low MTBF | Equipment fails often | Preventive maintenance, operating conditions, part quality, operator practices |
| High MTTR | Repairs take long | Spare parts availability, technician skills, diagnosis, vendor response |
| Both poor | Reliability and support problems | Consider replacement (repair-or-replace decisions) |
Break MTTR into parts to find delays: time to respond, time to diagnose, time waiting for parts, time to repair and time to restart. Waiting for parts is often the largest piece (spare parts management).
Data you need
- A clear definition of failure (any unplanned stop? stops longer than 10 minutes?)
- Scheduled operating time per asset
- Each failure recorded with start and end time
- Repair details from work orders: response, parts, cause (maintenance work orders)
Without recorded failures and times, MTBF and MTTR are guesses. Start recording consistently before setting targets.
Improving MTBF
- Preventive maintenance on critical assets (preventive maintenance)
- Root cause analysis of repeat failures (root cause analysis tools)
- Operator care: cleaning, lubrication, early reporting of abnormalities
- Better parts and correct operating conditions
Improving MTTR
- Critical spares on hand
- Clear priorities and fast response for critical equipment
- Troubleshooting guides and technician training
- Vendor service agreements with response commitments
- Standard repair procedures for frequent failures
MTBF, MTTR and OEE
In production, availability is one of the three factors of OEE. Improving MTBF and MTTR directly raises OEE availability. See OEE and production KPIs and machine downtime tracking.
Where Cirquolus fits
The Cirquolus asset management system records service requests, engineering work and vendor service against each asset, building the failure and repair history behind MTBF and MTTR. Track them as reliability measures on KPI scorecards.
Frequently asked questions
What is MTBF?
Mean time between failures: the average operating time between breakdowns of repairable equipment.
What is MTTR?
Mean time to repair: the average time needed to restore equipment after a failure.
How do you calculate availability from MTBF and MTTR?
Availability = MTBF ÷ (MTBF + MTTR).
What is the difference between MTBF and MTTF?
MTBF applies to repairable items. MTTF applies to items that are replaced rather than repaired.
Bring this workflow to a Cirquolus demo.
Show us your current process, companies and branches. We will map it to the modules you need and propose a realistic rollout.